2D Cavitation simulation

2D Cavitation Simulation using Converge Cfd

Aim: The aim is to simulate a 2D cavitation geometry that is the Winkly-hoffer Geometry for two different pressure differences of 30 bar and 70 bar, then plooting the results in paraview and explaining the conclusion.

Winkly Hoppers geometry: A geometry where there is a sharp throat and a wide cross-section between the inlet and the outlet. The primary reason for the study is to look at the cavitation on fuel injectors. So here in converge cavitation is studied using a Vof i.e Volum of Fluid approach, its a subset of multiflow simulation. Since in this case we have both liquid and gas phasewe call it as a multiface flow problem.

In converge Cfd the conversion between liquid and gas is derived by

`(Dx)/(Dt)=(x1-x)/theta`

Dx/Dt tells us the rate at which the liquid is going to convert into vapour

Boundary setup

There are a total of 6 boundaries

Case setup:

• Time based application is used
• For liquid simulation IC14H30 is used
• Global treansport parameters are kept untouched
• In species for gas N2 and C14H30 is used and for liquid IC14H30 (tetradecane)
• Transcient , full hydrodynamic, compressible solver for gas and incompressible solver for liquid
• The end time for simulation is 0.0002 sec
• For the inflow boundary a pressure of 100Pa is used and 30Pa for outflow to create a difference of 70Pa.
• In regions and initializations a nozzle region is formed at temp of 300K
• RNG k-ε is used as turbulence model
• For Volume of Fluid model cavitation model is used
• A base grid of 4e-5 is selected
• For adaptive mesh refinement nozzle region is used as active region max embed used is 3 and subgrid scale used is 0.1

Fixed embeding is used

The output file is selected as below

Governing equation:-

The solution for CFD simulation is obtained by solving the Navier-Stokes (NS) equations. The equations comprise of 5 equations, namely the continuity, momentum (3 equations), and energy equations. The continuity and momentum equations are solved for all flow problems with the energy equation are optional and can be used only when heat transfer is taking place to save computation time.

Here we assume that there is no heat transfer and that the temperature is constant, leaving us with 4 equations now, the continuity, and 3 momentum equations, one for each axis direction

Both the cases are then run using the cygwin terminal window , and post converted using the same

Image of surface with edges

Animation on velocity magnitude for a difference of 70 bar

Animation on Alpha for a difference of 70 bar

Animation on IC14H30 for a difference of 70 bar

Animation on velocity magnitude for a difference of 30 bar

Animation on Alpha for a difference of 30 bar

Animation on IC14H30 for a difference of 30 bar